1. Field of the Invention
This invention relates generally to a sewing apparatus with a cassette mount to which a thread cassette is detachably attached, and more particularly to such a sewing apparatus in which a threading mechanism is rendered inoperative when the thread cassette is attached to the cassette mount while the apparatus is shut off.
2. Description of the Related Art
There has conventionally been proposed a sewing apparatus which includes a cassette mount to which a thread cassette accommodating a thread spool is detachably attached and in which a thread drawn from the thread cassette serves as a needle thread. In the sewing apparatus, the thread drawn from the thread cassette attached to the cassette mount is caught between a pair of thread tension discs of a thread tensioning mechanism. The thread extending downstream from the thread tension discs is caught on a needle thread take-up lever, and the thread extending downstream from the lever is passed through an eye of a sewing needle mounted on a needle bar.
The assignee of this application filed a Japanese patent application assigned with Application No. 2002-91558 and relating to a sewing apparatus including a thread carrying mechanism and a threading mechanism each operated in synchronization with attachment of the thread cassette to the cassette mount. The thread drawn from the thread cassette is automatically passed through the needle eye by the thread carrying mechanism and threading mechanism. In the disclosed sewing apparatus, the thread drawn from the thread cassette is caught and carried near the needle eye by the thread carrying mechanism, and the carried thread is caught by the threading mechanism to be passed through the needle eye.
In the above-described threading mechanism, a threading shaft is descended to be positioned relative to a needle bar. The threading shaft is rotated so that a threading hook is passed through a needle eye. A thread drawn from the thread cassette is carried near the needle eye by a thread carrying mechanism. The thread is caught on a distal end of the threading hook having been passed through the needle eye. The threading shaft is then rotated in the opposite direction so that the threading hook is returned through the needle eye. As a result, the thread is passed through the needle eye.
In the above-described sewing apparatus, a needle bar vertically moving mechanism is vertically moved. However, in order that passing the thread through the needle eye by the threading mechanism may be realized, the thread cassette needs to be attached to the cassette mount and the threading mechanism needs to be operated while the needle bar is stopped at a predetermined vertical position so that the needle eye is prevented from entering the interior of the sewing bed.
A needle bar rocking mechanism is provided for rocking the needle bar in the foregoing sewing apparatus. The needle bar is supported on a needle bar mount to be vertically moved. The needle bar mount is mounted on a frame so as to pivot about a horizontal axis. The threading mechanism is provided on the needle bar mount so as to be rocked together with the needle bar. The thread carrying mechanism is provided on the frame on which the needle bar mount is pivotally mounted. The thread carrying mechanism is not rocked in such a manner as the needle bar or the threading mechanism.
Accordingly, positional relations between the thread carrying mechanism and the needle bar and threading mechanism vary. The varied positional relations further vary the percentage of success in passing the thread through the needle eye by the threading mechanism. A zigzag position of the needle bar is previously set to improve the success percentage. In order that passing the thread through the needle eye by the threading mechanism may be realized, the needle bar needs to be stopped at a predetermined vertical position as described above and moreover, the thread cassette needs to be attached to the cassette mount and the threading mechanism needs to be operated while the needle bar is stopped at a predetermined vertical position.
The needle bar vertically moving mechanism and the needle bar rocking mechanism are operable when electric power is being supplied to the sewing apparatus. Accordingly, the needle bar can automatically be moved to a suitable position (a predetermined vertical position or predetermined zigzag position) for the attachment of the thread cassette to the cassette mount. Or, when the vertical position of the needle bar is unsuitable for threading, informing the user of that is suggested for the purpose of preventing attachment of the thread cassette to the cassette mount.
However, when the sewing apparatus is disconnected from the power supply or is forgotten to be connected to the power supply, for example, the needle bar cannot be moved to a predetermined position by the needle bar vertically moving mechanism and threading mechanism or informing cannot be carried out. As a result, there is a possibility that the thread cassette may be attached to the cassette mount while the needle bar is stopped at a position other than the predetermined one.
Thus, the threading mechanism is operated in synchronization with the attachment of the thread cassette in the foregoing sewing apparatus. Accordingly, in a case where the thread cassette is erroneously attached to the cassette mount during shutoff from power supply, the threading mechanism is operated even when the needle bar is stopped at a position other than the predetermined one. Consequently, the threading mechanism may be damaged or other failure may occur. As the other failure, for example, the sewing machine cannot be threaded since the needle bar is not stopped at the predetermined position. Nevertheless, the thread is uselessly drawn from the thread cassette by the threading hook and the thread carrying mechanism when the threading mechanism is operated. It is time-consuming to rewind the drawn thread onto the thread spool in the thread cassette.
Therefore, an object of the present invention is to provide a sewing apparatus in which the threading mechanism is not operated in a case where the thread cassette is attached to the cassette mount when the apparatus is disconnected from the power supply, thereby preventing any disadvantage due to inadvertent operation of the threading mechanism during disconnection from the power supply.
The present invention provides a sewing apparatus comprising a needle bar on which a sewing needle is mounted, a needle bar vertically moving mechanism vertically moving the needle bar, a thread cassette having a thread accommodating section accommodating a supply of thread, a cassette mount to which the thread cassette is detachably attached, a threading mechanism operated in synchronization with attachment of the thread cassette to the cassette mount when the needle bar is stopped at a predetermined position, the threading mechanism passing the thread drawn from the thread cassette through an eye of the needle mounted on the needle bar, and a threading limiting unit limiting the threading mechanism so that the threading mechanism is inoperative in a case where the thread cassette is attached to the cassette mount when the apparatus is disconnected from a power supply.
In the above-described sewing apparatus, the threading mechanism is operated in synchronization with attachment of the thread cassette to the cassette mount when electric power is being supplied to the apparatus. In a case where the threading mechanism is operated when the needle bar is stopped at the predetermined position, the thread drawn from the thread cassette attached to the cassette mount is passed through the eye of the needle mounted to the needle bar. Furthermore, while electric power is being supplied to the apparatus, the threading mechanism is limited by the threading limiting unit so that the threading mechanism is inoperative, although the needle bar cannot automatically be moved to the predetermined position by the needle bar vertically moving mechanism and an alarming or informing operation cannot be performed.
In a preferred form, the sewing apparatus further comprises a needle bar rocking mechanism for rocking the needle bar and a needle bar movement controlling unit controlling the needle bar vertically moving mechanism and the needle bar rocking mechanism so that the needle bar is moved to the predetermined position in a case where the thread cassette has been detached from the cassette mount while electric power is being supplied to the apparatus. In this case, the needle bar movement controlling unit may control only the needle bar vertically moving mechanism.
In another preferred form, the threading mechanism includes a moving member provided on the cassette mount, the moving member being thrust by the thread cassette attached to the cassette mount thereby to be moved from an initial position so that the threading mechanism is operated, and the threading mechanism includes a holding unit holding the moving member at a standby position where the threading mechanism is inoperative even when the moving member is thrust by the thread cassette being attached to the cassette mount.
In further another preferred form, the holding unit includes a stopper engaging the moving member located at the standby position to hold the moving member at the standby position, an actuator switching between an engagement position where the stopper engages the moving member and a non-engagement position where the stopper is disallowed to engage the moving member, and a control unit controlling the actuator.
In the above-described construction, the actuator preferably comprises a pulse motor provided in the needle bar vertically moving mechanism for rocking the needle bar, and the threading limiting unit preferably limits the threading mechanism so that the stopper is located at the non-engagement position when the needle bar is located at the predetermined position and so that the stopper is located at the engagement position when the needle bar is located at a position other than the predetermined position.
In the above-described construction, the pulse motor preferably also serves to open and close a thread tension disc applying a tension to the thread drawn from the thread cassette, and the thread tension disc is preferably opened when the needle bar is located at the predetermined position and closed when the needle bar is located at a position other than the predetermined position.
In further another preferred form, the sewing apparatus further comprises a thread carrying mechanism operated in synchronization with attachment of the thread cassette to the cassette mount when the needle bar is stopped at the predetermined position, thereby carrying the thread from the thread cassette to a position near an eye of the needle mounted on the needle bar, and a limiting unit limiting the threading mechanism and the thread carrying mechanism so that both the threading mechanism and the thread carrying mechanism are inoperative in a case where the thread cassette is attached to the cassette mount when the apparatus is disconnected from a power supply.